PRESSURE RETARDED OSMOSIS: Making energy from freshwater flowing into saltwater

The latest episode in the American Chemical Society’s (ACS’) award-winning Global Challenges/Chemistry Solutions podcast series describes a process that could pave the way for a new genre of electric power-generating stations. These stations could supply electricity for more than a half billion people by tapping just one-tenth of the global potential of a little-known energy source that exists where rivers flow into the ocean.

Based on a report by Menachem Elimelech, Ph.D., and Ngai Yin Yip in the ACS journal Environmental Science & Technology, the new podcast is available without charge at iTunes and from www.acs.org/globalchallenges.

In the report, Elimelech and Yip explain that the little-known process, called pressure-retarded osmosis (PRO), exploits the difference in saltiness between freshwater and seawater. PRO requires no fuel, is sustainable and releases no carbon dioxide (the main greenhouse gas).

In PRO, freshwater flows naturally through a special membrane to dilute seawater on the other side. The pressure from the flow spins a turbine generator and produces electricity. The world’s first PRO prototype power plant was inaugurated in Norway in 2009. With PRO appearing to have great potential, the scientists set out to make better calculations on how much it actually could contribute to future energy needs under real-world conditions.

Elimelech and Yip concluded that PRO power-generating stations using just one-tenth of the global river water flow into the oceans could generate enough power to meet the electricity needs of 520 million people, without emitting carbon dioxide. The same amount of electricity, if produced by a coal-fired power plant, would release more than 1 billion metric tons of greenhouse gases every year.

Global Challenges/Chemistry Solutions is a series of podcasts describing some of the 21st century’s most daunting problems, and how cutting-edge research in chemistry matters in the quest for solutions. Global Challenges is the centerpiece in an alliance on sustainability between ACS and the Royal Society of Chemistry. Global Challenges is a sweeping panorama of global challenges that includes dilemmas such as providing a hungry and thirsty world with ample supplies of safe food and clean water, developing alternatives to petroleum to fuel society, preserving the environment and ensuring a sustainable future for our children and improving human health.

The American Chemical Society is a nonprofit organization chartered by the U.S. Congress. With more than 164,000 members, ACS is the world’s largest scientific society and a global leader in providing access to chemistry-related research through its multiple databases, peer-reviewed journals and scientific conferences. Its main offices are in Washington, D.C., and Columbus, Ohio.